Field of the Invention
The invention concerns additive compositions and lubricating compositions for use in a low phosphorus environment, which provide excellent phosphorus retention and improved resistance to lead and copper corrosion.
Discussion of the Prior Art
Government regulations over the last several decades have required Original Equipment Manufacturers (OEMs) to improve fuel economy and reduce pollution emissions for gasoline and diesel powered vehicles. It is common knowledge that OEMs and lubricant companies expect government to mandate even stricter fuel economy and emission requirements in the future. Many, if not all, of the vehicles now on the road contain pollution control devices to reduce pollution.
Engine oils are formulated with antioxidants, friction modifiers, dispersants and antiwear additives to improve vehicle fuel economy, cleanliness and wear. Unfortunately, many of these additives contribute to the fouling of the pollution control devices. When this occurs, vehicles emit high levels of pollution because of the failing performance of the pollution control devices.
It has been determined that high levels of phosphorus, sulfur and ash in gasoline and diesel engine oils can negatively affect the performance of pollution control devices. Not only is the level of phosphorus in engine oil important for the proper performance of pollution control devices but also phosphorus volatility. Phosphorous volatility can have a significant negative impact on the performance of pollution control devices. For example, phosphorus compounds with a high level of phosphorus volatility will have a greater negative impact on the performance of vehicle pollution control devices than phosphorus compounds with a low level of phosphorus volatility. New gasoline and diesel engine oil specifications require engine oils to contain low levels of phosphorus, sulfur and ash to protect the pollution control devices. Unfortunately, the antiwear additives used in engine oils to protect the engine contain sulfur and phosphorus. To ensure proper wear protection for gasoline powered engines and the pollution control equipment, GF-5, the most recent engine oil specification for gasoline powered vehicles, specifies a phosphorus range of 600 and 800 ppm and phosphorus volatility retention of at least 79% minimum.
Molybdenum additives are well known to those skilled in the art of oil formulation to act as friction modifiers to reduce engine friction and thereby improve vehicle fuel economy. However, it is also well known that high levels of molybdenum in engine oil can cause engine corrosion and wear. When this occurs, engine life expectancy is greatly reduced.
U.S. Pat. No. 6,806,241, which is incorporated herein by reference, teaches a three-component antioxidant additive comprising: (1) an organomolybdenum compound, (2) an alklyated diphenylamine and (3) a sulfur compound being a thiadiazole and/or dithiocarbamate.
U.S. Pat. No. 5,840,672, which is incorporated herein by reference, describes an antioxidant system for lubrication base oils as a three-component system comprising (1) an organomolybdenum compound, (2) an alkylated diphenylamine and (3) a sulfurized olefin and/or sulfurized hindered phenol.